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Scan Manual

2.0 - SCAN - Variant Spectrometer Interface Program

This program will acquire data from a Variant century series spectrometer and store the data in a binary, ASCII, or group file. The program is operated by using the arrow keys or tab keys to select an item from a menu at the top of the screen, and pressing the Enter key to select that item. This manual is organized by menu layer and option.

 

2.0.1The data screen
2.0.2Using the menus
2.0.3Selecting a page number
2.0.4Function keys

 

These features are identical to those found in the Epr.exe program data screen and is described in section(s) .1.0.X.

 

2.0.5 Operation notes

THIS PROGRAM DOES NOT CONTROL ANY FUNCTION OF THE EPR SPECTROMETER. This program acquires data passively from the spectrometer; it does not "drive" the field sweep of the spectrometer, control the sweep speed or width. The only experimental information the computer automatically stores is the sweep time, the number of scans, the day's date, and the day's time. Because of this, all functions of the Variant spectrometer platen are usable during the scan. The scan may be interrupted, the rate changed, and the scan resumed. In addition, an external sweep device may be used as long as that device either 1) sweeps the Variant platen, or 2) produces 1,000 independent TTL voltage steps which can be wired into the DT2801 external clock input.

 

2.0.6 Interface notes

The Variant spectrometer scans "approximately 10000" field steps in a full sweep. However, in our experience, the interval of these steps varied by such a degree as to sometimes 'bomb' the computer when two steps occurred too close together. We therefore have converted to using the C1024 interface line which pulses approximately 1024 steps across the scan. At each step, the program executes an analog to digital conversion of the DC EPR signal. When either the right limit or the 1024th step occurs, the computer's scan ends. The data is converted to exactly 1024 steps without changing the field scale. The Variant J1007 burndy plug is used for the sweep start, field step, spectrometer release, and ground level lines. Either the J1007 or the J307 coaxial can be the source of the DC EPR signal. This signal ranges from roughly positive 0.5 Volts to negative 0.5 Volts across the platen with the signal channel 10X switch off; it ranges +/-5.0 V with the 10X switch on. The signal does not clip at the limits of the platen.

 

2.0.7 Smooth signals

The default data acquisition setup assumes a moderately intense signal at a gain setting greater than 103. If you have a strong signal with a lower gain, you may see the digital effects of the AD converter. This will show up as un- smooth signals. To fix this problem, access the Control item of the Scan menu. Now raise the Gain of the AD converter and correspondingly raise the channel multiplier. Be aware that as you raise the Gain of the AD converter, you lower the maximum allowable signal height. To maintain a constant signal height, use these combinations:

 

GainMultiplierMax. detectable signal
02.0+/- 10.0 V
14.0+/- 5.0 V
28.0+/- 2.5 V
416.0+/- 1.25 V

 

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2.1.0 The main scan menu

File Display Layout Plot EXIT [Scan] These are the main menu options available to the user you. In general the main menu options have the following functions: The File, Display, Layout, and Plot, functions are identical to those of the Epr.exe program. See sections 1.1.x for details. The scan functions are explained in more detail below.

2.2.0 Scan Functions

Initiates the start of the computer scan. Switch the spectrometer into repeat mode and press the fast left button on the platen to start the scan. The program will wait for the left limit of the Variant platen before actually acquiring data. The scan will continue until either the right limit of the platen is reached or 1024 data points have been acquired. You may pause the scan, change the scan rate, the gain, the offset, etc... during the scan. Press F10 to stop the data acquisition.

 

Control

Change the computer interface specifications. The default values conform to one magnetic field scan.

 

Number of scans1 to 99
Type of scanM, K, S
Magnet sweep of the magnetic field
Kinetic constant magnetic field
Split Acquire an additional signal with the scan such as HPLC, Clark electrode, etc...
Scan offset1 to 9, 5= center. The display starting point for the first data of the scan.
Save every scanN = average scans, Y = save each scan to a separate disk file.
Wait for promptN = acquire each scan sequentially. Y = wait for the user to confirm each scan.
Save scans filename1 to 8 character filename for saving each scan separately. Example: test produces test.001, test.002, test.003, etc....
Split scan identifierText to identify the source of the additional signal.
Data offsetY-offset for the split scan.
Relative gainY-multiplier for the split data relative to the EPR data.
Delay time (s)Time in seconds of the delay between the EPR detection and the split scan detection. Computer acquisition is concurrent, this value affects display only.

 

Interface

Parameters to control the Analog and Digital connection between the computer and spectrometer. You will be prompted for a short list of inputs controlling the DT2801 data acquisition card. The default conditions are for a straight connection with no additional impedances. Gain code for A/D 1 to 4. The range of allowable voltages for each gain code is printed on screen as a guide to which gain code to select. The A/D converter will clip when the range is exceeded. The platen has a range of about -0.5 to +0.5 Volts. HOWEVER the range output by the J1007 or J307 signal lines will exceed these values and is dependent on whether the special x10 multiplier on the signal channel is on or off. The default is 1. 1st chan. multiplier 0.1 to 100.0 2nd chan. multiplier 0.1 to 100.0 These inputs allows you to correct for the needed scale of your data. A/D conversions at gain code 1 produce values one half as intense as at gain code 2, and so on. The default is 2.0 Signal channel start: 0 to 7 This is the differential input connect for the EPR channel. The second channel input is this value plus one. The default is zero. Use external trigger? Y or N A trigger is used to initiate the scan. If disabled, the program will begin acquiring data as soon as directed from the keyboard. If enabled, a trigger must be connected to the trigger input of the DT2801 board. Use external clock? Y or N The clock times the experiment. If external clock is selected, a clock must be connected to the external clock input of the DT2801 board. The period of the internal clock is set by the internal clock frequency. Internal clock time? 0.5 to 256 minutes. The total acquisition time needed when using an internal clock. This is the time for all data points to be collected. Number data steps? 128 - 4096. The number of data steps expected by the program.

 

Test

This entry will test the operation status of the DT2801. If this selection repeatedly produces error messages or hangs the machine, there is an error with the DT2801, probably the selection of the base address. The program is only configured to recognize the factory configuration base address of hexadecimal 2EC.

 

Measure

Continuous display of the EPR signal level. Press F10 to exit.

 

Parameters

This enables entry of record keeping parameters. These values DO NOT control the operation of the spectrometer. The scan time, time of day, date, and number of scans parameters are automatically generated by the program. If the scan type (M,K,S) is set to S the display will change. The scan time value will have an effect on the display IF a split scan was acquired AND a delay time not equal to zero was entered.

 

Directory

Changes the current data directory and/or views the contents of the directory.

 

Save_scan

Saves the scan to disk as a binary data file. You will be prompted for a file name.

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